Wall contacting tool

ABSTRACT

A drill string wall contacting tool, suitable for deviation control and/or bit stabilization is provided with replaceable wall contacting elements. Generically the tool is of the rotating fixed blade stabilizer type wherein the wall contacting elements rotate with the drill string but are fixed relative thereto, there being fluid passages in the sides of the tool which divide it azimuthally into a plurality of blades at whose periphery are the wall contacting surfaces. Preferably the tool is a four bladed stabilizer of the species known as a square drill collar. The wall contacting tool is grooved longitudinally at its outermost periphery. i.e., the corners of the square drill collar, and includes field replaceable wear elements received in the grooves and secured in place by radially-directed screws engaging holes in locking dowel pins releasably carried by the tool. The dowel pins extend into engagement with transverse mortises in the wear elements. There is more clearance between the screws and wear elements than between the dowel pins and wear elements so that all loads on the wear elements in the direction of the length of the grooves are taken by the dowel pins rather than the screws. Since the sides of the grooves take all loads on the wear elements in the direction tangent to the tool periphery, the screws are not required to take any load transverse to the screw axis. There is sufficient clearance to insure equal tightness of both sides of the wear elements with the adjacent grooves as the screws are tightened. Angle tolerances are set to insure initial contact of wear elements and tool at the outer periphery of the tool to insure lateral tightness of the wear elements in the groove, thereby to prevent fretting. In the case of a square drill collar, in order to provide greater depth to each rabbet and a larger arcuate wall contacting surface for each wear element, and at the same time allow sufficient longitudinal fluid passage space between the wear elements, the sides of the collar between the rabbets are relieved as compared to the flat sides of the usual square drill collar.

United States Patent 9 Garrett WALL CONTACTING TOOL [75] Inventor: William R. Garrett, Midland, Tex.

[73] Assignee: Smith International Inc., Midland,

Tex.

[22] Filed: Nov. 8, 1971 21 Appl. No.: 196,815

Related U.S. Application Data [63] Continuation of Ser. No. 38,715, May 19, 1970,

abandoned.

[52] US. Cl. 175/325 [51] Int. Cl. E211) 17/10, E21c 9/00 [58] Field of Search 308/4 A, 6 A; 175/320,

[56] References Cited UNITED STATES PATENTS 2,084,421 6/1937 Wright 175/325 X 2,088,770 8/1937 Skinner 175/320 X 2,589,534 3/1952 Buttolph 175/325 X 2,973,996 3/1961 Self 175/323 X 3,326,305 6/1967 Garrett et al. 175/76 X 3,454,308 7/1969 Kennedy 175/325 X 3,545,825 12/1970 Hamilton 308/6 A Primary Examiner-David H. Brown Attorney, Agent, or Firm-Murray Robinson [57] ABSTRACT A drill string wall contacting tool, suitable for deviation control and/or bit stabilization is provided with replaceable wall contacting elements. Generically the toc il is of the rotating fixed blade stabilizer type wherein the wall contacting elements rotate with the June 25, 1974 drill string but are fixed relative thereto, there being fluid passages in the sides of the tool which divide it azimuthally into a plurality of blades at whose periphery are the wall contacting surfaces. Preferably the tool is a four bladed stabilizer of the species known as a square drill collar. The wall contacting tool is grooved longitudinally at its outermost periphery. i.e., the corners of the square drill collar, and includes field replaceable wear elements received in the grooves and secured in place by radially-directed screws engaging holes in locking dowel pins releasably carried by the tool. The dowel pins extend into engagement with transverse mortises in the wear elements. There is more clearance between the screws and wear elements than between the dowel pins and wear elements so that all loads on the wear elements in the direction of the length of the grooves are taken by the dowel pins rather than the screws. Since the sides of the grooves take all loads on the wear elements in the direction tangent to the tool periphery, the screws are not required to take any load transverse to the screw axis. There is sufficient clearance to insure equal tightness of both sides of the wear elements with the adjacent grooves as the screws are tightened. Angle tolerances are set to insure initial contact of wear elements and tool at the outer periphery of the tool to insure lateral tightness of the wear elements in the groove, thereby to prevent fretting. 1n the case of a square drill collar, in order to provide greater depth to each rabbet and a larger arcuate wall contacting surface for each wear element, and at the same time allow sufficient longitudinal fluid passage space between the wear elements, the sides of the collar be tween the rabbets are relieved as compared to the flat sides of the usual square drill collar.

19 Claims, 11 Drawing Figures PATENTEnmzsmm SHEET 1 BF 5 FAVOR Afli' INVENTOR.

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ATTORNEY 1 WALL CONTACTING TOOL CROSS REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION a. Field of the Invention This invention pertains to earth boring equipment used in the rotary system of drilling and more particu larly to drill string wall contacting tools, for deviation control and/or bit stabilization, such as rotating, fixed blade stabilizers, and especially to so called square drill collars used in packed hole drilling. The invention concerns field replaceable wall contacting elements for.

such tools.

There are two general types of drill string stabilizers, the non-rotating type and the rotating type. The nonrotatlng type of stabilizer employs a wall contacting member having an axial bore. Rotatably mounted in the bore is a mandrel connectable at its ends to other drill string members for rotation therewith while the wall contacting member can remain fixed in the hole except for axial motion up and down the hole as the drill string is run in and out of the hole and during drilling and other manipulations of the drill string. The rotating type stabilizer employs a member having means at its ends for making connection to other drill string elements for rotation therewith and carrying at its outer periphery wall contacting surfaces. The wall contacting surfaces of the stabilizer rotate with the drill string relative to the axis of the hole being bored. Though of general applicability, the present invention is particularly intended for rotating stabilizers.

In the rotary system ofdrilling employing a liquid circulating through the drill string and the annulus between the drill string and well bore, it is necessary that a stabilizer include not only fluid passage means therethrough to form part of the drill string flow passage but also fluid passage means therethrough to form part of the annulus fluid passage. The latter fluid passage means usually are at the outer periphery of the tool with the result that the wall-contacting portion of the tool is not continuous around the circumference of the tool but instead consists of a number of parts azimuthally spaced apart by the fluid passage means. Rotating stabilizers are further classifiable according to whether such wall contacting parts are formed as blades fixed relative to the remainder of the stabilizer or are formed as rollers mounted for rotation about axes eccentric to the central axis of the tool. In the latter case, even though the remainder of the tool rotates with the drill string, the wall contacting portions of the tool roll on the wall of the well bore. This is in contrast with the wall contacting portions of fixed blade rotating stabilizers which must slide over the wall of the well bore as the drill string rotates. The present invention is especially intended for stabilizers of the latter rotating fixed blade type.

The usual stabilizer is of short length compared to the length of drill pipe and drill collars; for example, a stabilizer may be three feet long as compared to 30 feet for the length of a drill pipe or drill collar. The purpose of such a short tool is simply to center the drill string. However, it is also known to combine a stabilizer with a drill collar. The functions of a drill collar include providing weight at the lower end of the drill string and also providing rigidity to the lower end of the drill string. To achieve such functions drill collars have great wall thickness as compared to drill pipe, the Outer diameter of a drill collar being only enough smaller than hole bore to provide an adequate annulus for fluid passage. This is in contract with the construction of an ordinary stabilizer wherein the wall thickness of the portion of the tool providing an internal fluid passage is considerably less than that of a drill collar in order that the fluid passages between the blades be as large as possible.

The combination of the functions of a rotating fixed blade stabilizer and a drill collar results in a structure known as a square drill collar, a thick walled member of more or less square cross section the diagonals between corners being of full hole-bore diameter, the corners being rounded to provide more extended wall contacting surfaces than sharp corners would provide, the flats at the sides of the collar providing exterior (annulus) fluid passages. Such a thick walled member is especially adaptable to the present invention.

In point of fact, to provide rigidity and weight, a drill collar should be a long member, but because of resemblance to square drill collars in cross sectional shape and wall thickness, certain rotating fixed blade stabilizers are called short square drill collars. The present invention is equally applicable to short square drill collars and to ordinary square drill collars having a length comparable to that of round drill collars.

b. Description of Prior Art In the case of a wall contacting tool of the rotating, fixed blade type, such as a square drill collar, the portion of the tool that contacts the hole wall slides relative to the surface of the hole wall as the drill string rotates in the hole and is thereby subject to much more abrasion than a tool which slides over the hole wall only when the tool moves axially in the hole. When the wall contacting surface of the tool wears away, the axis of the tool can move to a position substantially eccentric to the hole axis prior to the tool contacting the wallof the hole, so that the tool no longer performs its function. To prolong the life of such a tool it is known to apply tungsten carbide or other hard material to the wall contacting surfaces of the tool; however even tools provided with hard surfaces may wear out rapidly when used in hard abrasive formations. When the stabilizers wall contacting surfaces wear out, they can be built back up by welding on new metal and hard facing material, but this requires that the tool be sent to a shop for such rebuilding. That means that a driller must carry an extra one or more of such tools in his stock of spare parts or risk being shut down pending repair of the wall contacting tool.

It is an object of the present invention to provide wall contacting tools having field replaceable wall contacting elements, to provide such tools that are economical to manufacture and which are reliable in use, the replaceable wear elements not being likely to come off and junk the hole. In the application of Sam Crews and Wendell Dixon entitled Wall Contacting Tool, Ser. No. 38,223, executed concurrently herewith and assigned to the same assignee as the present invention there is described a tool incorporating wear element disposed in right angle grooves and secured in place by two series of tangentially directed fasteners. The present invention uses a single series of radially directed fasteners and the grooves need not be rabbets.

SUMMARY OF THE INVENTION According to the invention the portions ofa wall contacting tool bearing hole wall contacting surfaces are made as separate parts from the remainder or body of the tool. Such separate parts constitute wear elements. The wear elements are fitted into correlative supporting grooves in the body of the tool which take tangential and radial inward loads imposed on the wear elements. The wear elements are releasably secured to the body by means including a series of radially directed dowel pins extending outwardly into transverse mortises in the wear elements to take loads parallel to the tool axis, the pins having logs releasably locked in the tool body and having threaded holes to engage screws extending through the wear elements to take radial outward loads. Preferably the grooves are V-grooves, i.e., grooves having two plane sides disposed at an angle to each other, with the bisector of the angle disposed in a radial plane relative to the tool axis, whereby tightening of the radially directed fastening means will draw or push each wear element against both sides equally of the correlative groove. The angle tolerances are adjusted to insure that when the fastening means is tightened the contact between the outer edge of each wear element and the correlative groove will occur before or at the same time but not after contact of the innermost part of the wear element and groove, thereby to insure that the element will be laterally tight in the correlative groove so as to avoid fretting. The clearances are such that the wear element can center itself between the two sides of the groove as the fastening means is tightened and so that the dowel pins will take all the loads parallel to the tool axis.

In preferred embodiments of the invention the wall contacting tool is in the form of a square drill collar and the releasable wear elements are faced with hard material such as tungsten carbide. The wear elements are each disposed in a groove at a corner of the collar where there is a maximum amount of wall thickness of the tool to receive the wear elements. By providing threaded holes in releasable dowels to receive the wear element fastening screws, it is not necessary to make blind threaded holes in the core of the tool, which is another advantage of the dowel pins.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a section through an earth formation illustrating several drilling assemblies using a variety of known wall contacting tools;

FIG. 2 is an elevation showing a short square drill collar embodying the invention; FIG. 3 is, a fragmentary horizontal section taken at planes 3-3 of FIG. 2;

FIGS. 3A and 3B are fragmentary sections similar to that of FIG. 3 showing modifications;

FIGS. 4 and 5 are respectively top and front views of a dowel pin used in the invention (shown in horizontal section in FIG. 3);

FIG. 6 is a fragmentary elevation, partly in section, of the tool shown in FIG. 2, but to a larger scale;

FIG. 7 is an elevation showing a square drill collar embodying the invention; and

FIGS. 8 and 9 are enlarged fragmentary side elevations of the tool shown in FIG. 8 and viewed at planes 88 and 99 indicated on FIG. 8.

Referring first to FIG. 1 there is shown a vertical section through an earth formation penetrated by five bore holes l1l5. In hole 11 is shown a drilling assembly suitable for small diameter bore holes in softer formations, i.e., soft to medium hard, and including a'roller cutter reamer-stabilizer 17 (see US. Pat. No. 3,306,381 issued Feb. 28, 1967, on the application of W. R. Garrett et al.) adjacent to drill bit 18, an ordinary round drill roller 19, a non-rotating blade stabilizer 20 (see US. Pat. Nos. 3,063,759 and 3,320,004 issued Nov. 13, I962 and May 16, 1967 on the applications of S. C. Moore et al. and W. R. Garrett, respectively) another round drill collar 21, and another non-rotating, blade stabilizer 22.

In hole 12 is shown a drilling assembly suitable for small diameter bore holes in harder formations, i.e., hard to medium hard, and including three helical fixed blade rotating stabilizers 30, 31, 32 (see US. Pat. No. 3,285,678 issued Nov. 15, 1968, on the application of W. R. Garrett et al) separated by ordinary round drill collars 33, 34, the lowermost stabilizer 32 being adjacent drill bit 35.

In hole 13 is shown a drilling assembly suitable for medium diameter bore holes inharder formations and including adjacent the bit 40 a roller cutter reamerstabilizer 41, a pair of fixed blade rotating stabilizers 42, 43 and a plurality of round drill collars 44, 45.

In hole 14 is shown a drilling assembly suitable for medium diameter bore holes in softer formations including above the bit 50 a short square drill collar 51, a plurality of helical fixed blade stabilizers 52, 53, 54, and ordinary round drill collars 55, 56.

In hole 15 is shown a drilling assembly suitable for large diameter bore holes in harder formations and including adjacent drill bit 60 a roller cutter reamerstabilizer 61, a square drill collar 62, and a pair of blade stabilizers 63, 64 and an ordinary round drill collar 65.

Referring now to FIGS. 2 and 3 there is shown a wall contacting tool in the form of a short square drill collar including an internally threaded tapered box 101 at its lower end providing means for making a rotary shouldered connection to an externally threaded tapered pin on a drill bit and including an internally threaded tapered box 102 at its upper end providing means for making a rotary shouldered connection to an externally threaded tapered pin on another drill string member. The smooth cylindical unthreaded exterior portion 103 of box 102 provides a tong engageable surface for use in making and breaking the threaded connections at the ends of the tool. Since the tool is typically only about three feet long, only one such surface is needed for making and breaking connection at both ends of the tool. The portion of the tool below box 102 and tong surface 103 may be called the tool body. The tool may be described as being an elongated, generally cylindrical member having a plurality of, preferably four, longitudinally extending grooves 104 providing external fluid passage means to allow drilling fluid to flow past the tool between the tool and the wall of a bore hole. The grooves 104 are illustrated as-being V section grooves having flat sides but other suitable shapes of cross section may be employed. Through the axis of the tool is a cylindrical hole 105 providing internal fluid passage means to allow drilling fluid to flow through the tool between drill string members connected at the ends of the tool.

The lower end of the tool has an annular bevel 110 and immediately adjacent thereto the outer periphery of the tool is provided with areas 111 of hard facing material, e.g., welded on sintered tungsten carbide. Additional areas 112 of hard facing material are disposed around the outer periphery of the tool adjacent the tong area 103. It will be noted that the body of the tool is of larger outer diameter than tong area 103, but the distance between the depths of opposing grooves 104 is less than the tong area diameter. With an ordinary square drill collar the distance between opposing flats would be as great or larger than the diameter of the tong area. However, it will be noted that even at the depths of grooves 103, the wall thickness X (FIG. 3) of the tubular tool is of the same order of magnitude as the inner diameter Y of the tool, which is characteristic of a drill collar and is one characteristic which distinguishes a square drill collar from other fixed blade rotating stabilizers.

Referring now to FIGS. 2, 3, and 6, extending substantially the full length of the body of the tool are a plurality of series of wear elements in the form of metal strips 120 disposed end to end in close proximity to each other but slightly spaced apart, the wear elements being received in correlative grooves 121. By way of example the grooves may be 3%. feet long and each wear element being 6 inches long or about the same length as the tool outer diameter; the use ofa plurality of short strips avoids difficulty with warpage that occurs when long strips are provided with hard surfaces. Preferably there are four such series of strips received in four such grooves. The grooves for the wear strips preferably extend continuously from adjacent one end of the body to adjacent the other end of the body, and are formed midway between the grooves 104 that provide the external fluid passages of the tool. Preferably the number of fluid passage grooves equals the number of wear strips and wear strip grooves. As shown, grooves 121 are rabbets, that is, they are V grooves having two planar sides that are perpendicular to each other. However V grooves having obtuse or acute angles between the sides also could be used and other shapes of grooves including curved grooves could be used, but V grooves and rabbets are preferable. The grooves are disposed so that the planes on the axes of groove symmetry, i.e., in the case of V-grooves the planes bisecting the angles of the grooves, are radial with respect to the tool axis.

Referring now particularly to FIGS. 3-6, each rabbet is provided with a series of sockets 130. The innermost portions of bottoms 131 of the sockets are cylindrical. The axes ofthe sockets lie in planes that are on the axes of symmetry of the grooves and since the grooves are disposed with their axes of symmetry radial, the axes of the sockets are also radial. The mouths or outermost portions 132 of the sockets are enlarged in the longitudinal direction relative to the tool body. Between the mouths and bottoms of the sockets the sockets are midportions 133 which are further enlarged laterally, relative to the mouths of the sockets, which, in view of the direction of the latter is, perpendicular to both the socket axis and the tool axis. The midportions 133 provide locking recesses as hereinafter explained.

Received within each socket is a locking dowel pin 135 including cylindrical ends 136, 137 and locking means in the form of lugs or ears 138 shaped to pass through the mouth 132 of the socket (with clearance space at each end) and fit neatly within the locking recesses 133 of the socket when turned transverse to the mouth 132. Each dowel pin 135 has a threaded hole 139 extending axially therethrough.

Each wear strip is provided with a plurality (two as shown) of holes 140 registering with threaded holes 139.

Each of the holes 140, is enlarged at its outer terminus 142 to receive the head of an Allen screw as will be described hereinafter. The inner terminus of each hole 140, is in the form of a slot 143 transverse to the hole and to the tool axis, the slot being wider than the hole diameter to receive the outer end of one of the dowel pins 135, thereby preventing movement of the wear strips axially relative to the tool body.

The dimensions of each of the sockets 130, dowels 135, and holes 140 are preferably equal to those of the other sockets, dowels, and holes, respectively, and the dimensions of each wear strip and rabbet are preferably the same as those of the other wear strips and rabbets, so that the wear strips are interchangeable.

The wear strips have cylindrically curved outer peripheries which may be case hardened as indicated at or, as shown in FIG. 3A, coated with hard facing material 151, similar to hard faced areas 111, 112 or, as shown in FIG. 33, can be provided with a plurality of cylindrical wear inserts 152 pressed into cylindrical sockets 153 and retained therein by peening over the mouths of the sockets.

The wear strips are secured against radially outward movement relative to the body of the tool by radially pointing Allen screws which pass through holes 140 into the threaded holes 139 in dowel pins 135. Screws 160 can be tightened to draw the strips against flat sides of each groove. The heads of the Allen screws bear against the shoulders formed by the junctures of the holes 140, with their enlarged outer ends 142, to draw the strips tightly against the sides of the rabbet grooves. There is sufficient clearance between the heads of the Allen screws and hole enlargements 142, and between the stems of the Allen screws and holes 140, and between the locking recesses 133 and lugs 138, to insure registry of the Allen screws with threaded holes 139 in the dowel pins 135 and allow the wear strips to centralize themselves between opposite sides 170 of the grooves to equalize the pressure against each side as the screws are tightened. In addition, the manufacturing tolerances on the angle between the sides of the rabbets and the angle between the sides of the wear strips are set to ensure that there is initial contact between the strip and groove at the outer edges 171 as soon as or at least before there is initial contact of the wear strip and groove farther in near the apex 173 of the wear strip. To avoid reference to manufacturing tolerances it may be stated simply that the apex angle'of each wear strip is as large or slightly larger than the apex angle of the correlative V-groove or rabbet. Apex 173 is spaced from the apex 174 of the groove for the same reason the result is that the strips are laterally tight in the grooves when the screws are tightened, thereby preventing fretting.

It is to be noted, as best shown in FIG. 6, that when each wear strip is in place in its rabbet, the apex portions of the wear strip above and below hole enlargement 143 extend above and below the dowel pin 135 into the path required for rotation of the locking lugs 138 about the dowel pin axis, thereby preventing the locking lugs from turning into the vertical or released position and holding them in the horizontal or locking position in locking recesses 133, and preventing the dowel pins from turning with the Allen screws 160 when the latter are rotated to tighten or release the wear strip.

The wear strips are of such radial extent as to extend beyond the generally cylindrical outer periphery 180 of the body of the tool 100. The diameter of the tool as measured between the wall contacting surfaces 150 of body of the tool. The edges 181, 182 of the strips that protrude beyond the sides of the rabbets are rounded so that the edges tend to slide over protuberances in the wall of the well bore, thereby preventing the strips from being torn off the tool.

The portions of the body of the tool at each end of the rabbets 121 flare out as shown at 190, 191 to flanges 192, 193 of the same diameter as the wear surfaces 150 to protect the ends of the strips from hanging up on wall protuberances as the tool is moved axially in the hole. These flanges also support and are protected by the hard facing 11], 112 at the ends of the tool.

Referring now to FIG. 7 there is shown a square drill collar 200 which may be of a length typical of drill collars, e.g., 30 feet. The tool is provided at each end with internally threaded boxes 201, 202, and has an internal axial flow passage 203. The outer periphery of the tool is generally cylindrical as indicated at 204 with axially extending shallow V grooves 205 providing external flow passages between the exterior of the tool and the wall of the well bore.

At intervals along the length of the tool, e.g., adjacent the upper and lower ends, the tool is provided with rabbets extending axially between the V grooves, and lying in these rabbets are series of short wear strips 207, 208 similar to the construction previously described as the first embodiment of the invention. The wear strips are hard faced at their outer peripheries to provide wall contacting surfaces. The hard facing of strips 207 is i1- lustrated as of the same type as disclosed in FIG. 38, shown in elevation in FIG. 9. The hard facing of the strips 208, 209 may be of the welded on sintered tungsten carbide type previously mentioned that is shown in FIG. 3A, shown in elevation in FIG. 8.

Typically, the series of wear strips 208 adjacent the upper end of the tool, and the series of wear strips 208 near the lower end of the tool, extend for about 3 feet, each individual wear strip 208 being about one-half foot in length; the lower-most series of wear strips 207 extend for about 1 foot, consisting of 2 6 inch strips. If desired, additional groups of wear elements can be disposed at intervals along the length of the collar between the groups at the upper and lower ends of the collar. The strips 207 are spaced from the strips 208 by an annular smooth cylindrical tong engageable surface 209 of a diameter intermediate between the minimum distance between opposite grooves 205 and the diamevided at the upper end of the tool above wear strips The wear strips 207, 208 and the manner of fastening same to the remainder of the tool are the same as in the first described embodiment of the tool. The wear strips are held in place by screws 211 engaging threaded holes in locking dowel pins (not shown).

As in the first described embodiment, the longitudinal edges 220, 221 of the wear strips are rounded to prevent the strips from hanging up as the tool rotates, and at the ends of the strips the full diameter portions, e.g., as shown at 230, 231, 232, 233, of the drill collar protect the strips from catching when the tool moves axially. Flaring portions, e.g., as shown at 235, 236, 237, 238, join such full diameter portions with the ends of the rabbets.

It will be noted that due to the fact V-groove passages are provided in the normally flat sides of the square drill collars of the embodiments of the invention heretofore described, and the fact that rounded corners of large arcuate extent are provided, the cross sections of the drill collars are scarcely square. In addition, although tools having four wall contacting elements at any level along the tool length have been described, the invention is also applicable to wall contacting tools having more or less than four wall contacting elements at any level along the length of the tool. Therefore, the subject tools might better be referred to as collarstabilizers, the word collar directing attention to the wall thickness without referring to any particular shape.

While preferred embodiments of the invention have been shown and described, variations thereof can be made by one skilled in the art without departing from the spirit of the invention.

I claim:

1. Wall contacting tool suitable for use in a drill string as an element thereof comprising a tubular body having internal fluid passage means extending from one end thereof to the other, means at the ends of said body for making connections with other drill string elements to transmit fluid and mechancial forces therebetween, ex-

terior fluid passage means formed by grooves in said tool body disposed spaced apart around the outer periphery of said tool body, the minimum radial distance between said internal and external fluid passage means being of the same order of magnitude as the minimum distance across said internal fluid passage means through the axis of said tool whereby the body of the tool has a generally realtively thick wall compared to the internal fluid passage therethrough, V section groove means in the outer periphery of said tool body between said fluid passage means, wall contacting means having an inner surface mating with said groove means and carried by said body disposed spaced apart around the outer periphery thereof in said grooves, and releasable fastening means securing said wall contacting means to said body, said releasable means extending radially through said wall contacting means into said wall of said body.

2. Tool according to claim 1 wherein said groove means extend axially along the outer periphery of the tool providing means to prevent radial inward and azimuthal movement of said wall contacting means relative to the axis of the tool, said fastening means preventing radial outward and axial movement of said wall contacting means relative to the axis of the tool.

3. Tool according to claim 2 wherein said releasable fastening means includes dowel means extending between said tool body and said wall contacting means, said dowel means preventing axial movement of said wall contacting means relative to the axis of said tool body.

4. Tool according to claim 2, said groove means having flat sides that are disposed at an angle to each other and said wall contacting means having flat sides correlative to those of said groove means, the plane bisecting the angle of said groove means being radially disposed and the axis of said releasable fastening means also bisecting said angle.

5. Tool according to claim 4 wherein said angle of said groove means is slightly smaller than the angle between the sides of the wall contacting elements to insure initial contacts of the wall contacting means with the outer edges of the groove means prior to contact of the wall contacting means with portions of the groove means closer to the apex of the angle thereof as said fastening means is tightened; thereby to insure that said wall contacting means is laterally tight in the groove so as to prevent fretting.

6. Tool according to claim 5 wherein the apex angle of each wall contacting element is rounded off and spaced from the bottom of the correlative groove.

7. Wall contacting tool suitable for use in a drill string as an element thereof comprising a tubular body having internal fluid passage means extending from one end thereofto the other, means at the ends of said body for making connections with other drill string elements to transmit fluid and mechanical forces therebetween,

groove means in the outer periphery of said tool body spaced apart therearound, wall contacting means carried by said body disposed spaced apart around the outer periphery thereof in said grooves, and releasable fastening means securing said wall contacting means to said body, said releasable means extending radially through said wall contacting means into said wall of said body,

said groove means extending axially along the outer periphery of the tool providing means to prevent radial inward and azimuthal movement of said wall contacting means relative to the axis of the tool, said fastening means preventing radial outward and axial movement of said wall contacting means relative to the axis of the tool,

said releasable fastening means including dowel means extending between said tool body and said wall contacting means, said dowel means preventing axial movement of said wall contacting means relative to the axis of said tool body,

said dowel means including:

radial sockets in said tool body,

aperture means in each wall contacting means at the groove engaging side thereof,

pins each extending from one of said sockets into one of said aperture means, and

lug means on each pin engageable with locking recess means in the associated one of said sockets to prevent withdrawal of the pin from the socket.

8. Tool according to claim 7 herein the releasable fastening means further comprises screw means extending through holes in said wall contacting means into holes in said pins.

9. Tool according to claim 8 wherein said wall contacting means includes portion interengaging with each of said lugs to prevent rotation of each of said lugs about the axis of the associated one of said pins.

10. Tool according to claim 8 wherein the clearances between said holes in said wall contacting means and said screw means exceed the clearances between said lug means and locking recesses at least in the direction of the axis of the tool body to relieve said screw means of axial loading.

11. Wall contacting tool suitable for use in a drill string as an element thereof comprising a generally tubular body providing internal fluid passage means extending from one end of the body to the other end thereof, means at each end of the body for making connection to another drill string element, wall contacting means carried by said body, groove means in said body receiving said wall contacting means; and fastening means extending through said wall contacting means radially into said tubular body releasably securing said wall contacting means in said groove means, said groove means being of V section and said wall contacting means having surfaces mating therewith, said fastening means bisecting the angle of said V section.

12. Tool according to claim 11, said groove means having undercut locking socket means at the bottom thereof to receive and hold one end of said fastening means.

13. Tool according to claim 12, said socket means being of generally cylindrical configuration with its axis radially disposed relative to the axis of the tool body, an entrance portion of said socket means, commencing at the mouth thereof and extending inwardly, being elongated in the direction of the axis of said body, a locking portion of said entrance portion disposed inwardly of the mouth of said socket means being also elongated transverse to the axis of said body and the axis of said socket means.

14. Tool according to claim 13 wherein said fastening means includes a dowel pin having lugs adapted to enter the entrance portion of said socket means and turn in said locking portion of said entrance means.

15. Tool according to claim 14 wherein said lugs protrude into said groove means and said wall contacting element is mortised to receive said lugs and prevent same from turning in said socket means.

16. Tool according to claim 14 wherein said dowel pin has a threaded hole extending axially thereof and said fastening means includes a screw extending radially through a hole in said wall contacting element into said threaded hole.

17. Square drill collar having at its corners elongate replaceable wall contacting elements of V section releasably secured thereto in longitudinally extending grooves of V section by fastening means extending radially realtive to said collar.

18. Collar according to claim 17 wherein each corner of the collar has a rabbet extending longitudinally of the collar, a plurality of said wall contacting elements being disposed in each rabbet in end to end closely adjacent relationship.

19. Collar according to claim 18, each wear element protruding radially beyond its groove, the longitudinal edges of each element being rounded. 

1. Wall contacting tool suitable for use in a drill string as an element thereof comprising a tubular body having internal fluid passage means extending from one end thereof to the other, means at the ends of said body for making connections with other drill string elements to transmit fluid and mechancial forces therebetween, exterior fluid passage means formed by grooves in said tool body disposed spaced apart around the outer periphery of said tool body, the minimum radial distance between said internal and external fluid passage means being of the same order of magnitude as the minimum distance across said internal fluid passage means through the axis of said tool whereby the body of the tool has a generally realtively thick wall compared to the internal fluid passage therethrough, V section groove means in the outer periphery of said tool body between said fluid passage means, wall contacting means having an inner surface mating with said groove means and carried by said body disposed spaced apart around the outer periphery thereof in said grooves, and releasable fastening means securing said wall contacting means to said body, said releasable means extending radially through said wall contacting means into said wall of said body.
 2. Tool according to claim 1 wherein said groove means extend axially along the outer periphery of the tool providing means to prevent radial inward and azimuthal movement of said wall contacting means relative to the axis of the tool, said fastening means preventing radial outward and axial movement of said wall contacting means relative to the axis of the tool.
 3. Tool according to claim 2 wherein said releasable fastening means includes dowel means extending between said tool body and said wall contacting means, said dowel means preventing axial movement of said wall contacting means relative to the axis of said tool body.
 4. Tool according to claim 2, said groove means having flat sides that are disposed at an angle to each other and said wall contacting means having flat sides correlative to those of said groove means, the plane bisecting the angle of said groove means being radially disposed and the axis of said releasable fastening means also bisecting said angle.
 5. Tool according to claim 4 wherein said angle of said groove means is slightly smaller than the angle between the sides of the wall contacting elements to insure initial contacts of the wall contacting means with the outer edges of the groove means prior to contact of the wall contacting means with portions of the groove means closer to the apex of the angle thereof as said fastening means is tightened; thereby to insure that said wall contacting means is laterally tight in the groove so as to prevent fretting.
 6. Tool according to claim 5 wherein the apex angle of each wall contacting element is rounded off and spaced from the bottom of the correlative gRoove.
 7. Wall contacting tool suitable for use in a drill string as an element thereof comprising a tubular body having internal fluid passage means extending from one end thereof to the other, means at the ends of said body for making connections with other drill string elements to transmit fluid and mechanical forces therebetween, groove means in the outer periphery of said tool body spaced apart therearound, wall contacting means carried by said body disposed spaced apart around the outer periphery thereof in said grooves, and releasable fastening means securing said wall contacting means to said body, said releasable means extending radially through said wall contacting means into said wall of said body, said groove means extending axially along the outer periphery of the tool providing means to prevent radial inward and azimuthal movement of said wall contacting means relative to the axis of the tool, said fastening means preventing radial outward and axial movement of said wall contacting means relative to the axis of the tool, said releasable fastening means including dowel means extending between said tool body and said wall contacting means, said dowel means preventing axial movement of said wall contacting means relative to the axis of said tool body, said dowel means including: radial sockets in said tool body, aperture means in each wall contacting means at the groove engaging side thereof, pins each extending from one of said sockets into one of said aperture means, and lug means on each pin engageable with locking recess means in the associated one of said sockets to prevent withdrawal of the pin from the socket.
 8. Tool according to claim 7 herein the releasable fastening means further comprises screw means extending through holes in said wall contacting means into holes in said pins.
 9. Tool according to claim 8 wherein said wall contacting means includes portion interengaging with each of said lugs to prevent rotation of each of said lugs about the axis of the associated one of said pins.
 10. Tool according to claim 8 wherein the clearances between said holes in said wall contacting means and said screw means exceed the clearances between said lug means and locking recesses at least in the direction of the axis of the tool body to relieve said screw means of axial loading.
 11. Wall contacting tool suitable for use in a drill string as an element thereof comprising a generally tubular body providing internal fluid passage means extending from one end of the body to the other end thereof, means at each end of the body for making connection to another drill string element, wall contacting means carried by said body, groove means in said body receiving said wall contacting means; and fastening means extending through said wall contacting means radially into said tubular body releasably securing said wall contacting means in said groove means, said groove means being of V section and said wall contacting means having surfaces mating therewith, said fastening means bisecting the angle of said V section.
 12. Tool according to claim 11, said groove means having undercut locking socket means at the bottom thereof to receive and hold one end of said fastening means.
 13. Tool according to claim 12, said socket means being of generally cylindrical configuration with its axis radially disposed relative to the axis of the tool body, an entrance portion of said socket means, commencing at the mouth thereof and extending inwardly, being elongated in the direction of the axis of said body, a locking portion of said entrance portion disposed inwardly of the mouth of said socket means being also elongated transverse to the axis of said body and the axis of said socket means.
 14. Tool according to claim 13 wherein said fastening means includes a dowel pin having lugs adapted to enter the entrance portion of said socket means and turn in said locking portion of said entrance means.
 15. Tool according to claim 14 wherein said lugs protrude into said groove means and said wall contacting element is mortised to receive said lugs and prevent same from turning in said socket means.
 16. Tool according to claim 14 wherein said dowel pin has a threaded hole extending axially thereof and said fastening means includes a screw extending radially through a hole in said wall contacting element into said threaded hole.
 17. Square drill collar having at its corners elongate replaceable wall contacting elements of V section releasably secured thereto in longitudinally extending grooves of V section by fastening means extending radially realtive to said collar.
 18. Collar according to claim 17 wherein each corner of the collar has a rabbet extending longitudinally of the collar, a plurality of said wall contacting elements being disposed in each rabbet in end to end closely adjacent relationship.
 19. Collar according to claim 18, each wear element protruding radially beyond its groove, the longitudinal edges of each element being rounded. 